CA1240095A - Ionically cross-linked siloxane polymers - Google Patents

Abstract

IONICALLY CROSS-LINKED SILOXANE POLYMERS
ABSTRACT OF THE DISCLOSURE
Siloxane polymers containing zwitterions on tertiary silicone atoms and their aminoalkyl siloxane polymer intermediates are provided. Methods of their production are also provided. The aminoalkyl siloxane polymer intermediates and the zwitterionic siloxane polymers are obtained by co-polymerizing trifunctional aminoalkyl silanes or zwitterionic silanes, respectively, with hydroxy-terminated siloxane oligomers in the presence of an acid catalyst. The aminoalkyl siloxane polymer intermediate are converted to zwitterionic siloxane polymer by reaction with an organosultone or an organo-lactone. Trifunctional aminoalkyl silanes are readily available and utilizing these silanes provides an economical route to obtaining zwitterionic siloxane polymers.

Description

- 1 - RD-15,201 IONIC~LLY CROSS-hINKED 'SIL'OX'~E POLYMERS
_ ''BA~KGROUND OF THE 'INVENTI'ON
This invention relates to ionically cross-linked siloxane polymers. More particularly, this invention relates to ionically cross-linked zwitterionic siloxane polymers having ionic corss-links at trifunctional silicone atoms and a method of their production.
Zwitterions are ions which are both positively and negatively charged. Common zwitterionic species are the amino sulfonates, NH2 -R-S03 and the amino carbonates, NH2 -R-COO ; wherein R is a divalent hydrocarbon radical more particularly defined below. Zwitterionic species are typically obtained from ionizing amino acids and the like;
however, siloxane polymers containing zwitterions have been prepared by Litt and Matsuda, J. Polymer Science, VolO 19, p. 1221 (1975) and by Graiver et al, J.Poly. Sci., Polymer,Chem. Ed., Vol. 17, p. 3559 (1975).
Litt and Matsuda disclose a process for producing zwittionic silanes by reacting the trifunctional aminoalkyl silanes, ~-aminopropyltriethoxysilane and N-aminoethyl- ~-amino-propyltrimethoxy silane, with ~-propane sultone.
Graiver et al disclose that siloxane polymers containing zwitterions can be obtained by treating an amlnoalkyl siloxane with ~-propane sultone. The aminoalkyl siloxanes are provided by copolymeriæing a dimethoxy silane having an aminoalkyl radical with a low molecular weight hydroxy-terminated polydimethylsiloxane . j .... .. -.

~ RD-1S,201 and decamethyl-tetrasiloxane.
The zwitterions on the siloxane polymers provide ionic cross-linking be-tween the siloxane polymers due to the coulombic forces exerted by the ions. An example of an ionic cross-link which may exist between two siloxane polymer segments is illustrated in the following formula:
Siloxane polymer backbone Siloxane polymer backbone Sl-R -NH2 -R-S03 ~ S03-R- NH2-R'-Si-wherein Rl is a divalent hydrocarbon radical of from 1 to 20 carbon atoms and R is a divalent hydrocarbon radical of from 2 to 20 carbon atoms.
These cross-links reduce the mobility of the polymer segments and increases their stiffness. For example, polydimethylsiloxane (DP = 500) are typically liquid at room temperature, yet corresponding zwitterionic polysiloxanes are solid rubbers at this temperature.
Introducing zwitterions to as few as 0.5~ of the silicone atoms within a siloxane fluid will provide a solid elastomeric material.
These elastomeric materials exhibit high adhesion to glass and other substrates such as, for example, wood, metal, polycarbonates, polystyrene, po]yphenylene oxides and blends thereof, etc. The elastomeric properties and adhesive properties of these zwitterionic silo~anes ma~e them suitable for use as adhesives, elastomeric adhesives, sealants, coatings, injection moldable and compression moldable rubbers and plastics, and various silicone based rubbers.
In the present state of the art, only difunctional silanes are utilized to obtain zwitterionic siloxane polymers having a degree of polymerization - 3 - RD-15,201 sufficiently high to provide the useful elastomeric materlals described above. Difunctional zwitterionic siloxanes are either copolymerized with dimethyl siloxane oligomers or difunctional aminoalkyl silanes are copolymerized with dimethyl siloxane oligomers and subsequen-tly reacted with ~ propanesultone to obtain the zwitterionic species on the siloxane polymers. It is difficult to prepare the difunctional zwitterionic silanes and the difunctional aminoalkyl silanes, which makes the production of zwitterionic siloxane polymers expensive. It is deslrable to utilize less costly precursors in the production of zwitterionic siloxane polymers.
Trifunctional aminoalkyl silanes are more readily available and less expensive than their difunctional counterparts. However, copolymerization of such trifunctional aminoalkyl silanes with dimethyl siloxane by conventional methods has been difficult, if not impossible, to achieve. Typically the trifunctional aminoalkyl silane polymerizes with itself to form a yellow precipitate and does not become incorpcrated within the siloxane polymer.
The present invention is based on the discovery of an effective method for copolymerizing the less expensive trifunctional aminoalkyl silanes or trifunctional zwitterionic silanes with siloxane oligomers to provide aminoalkyl siloxane polymer intermediates and zwitterionic siloxane polymers, respectively. Only a small quanti-ty of the trifunctional aminoalkyl silanes and trifunctional zwitterionic silanes homo polymerize in this process, which permits a greater proportion to be incorporated within the copolymer produced.
SUMMARY OF THE I_VENTI~ON
This invention provides zwitterionic siloxane polymers having at least about 0.5~ of the silicon atoms chemically combined in accordance with the formula - 4 - RD-15,201 R -Si(~)3 and aminoalkyl siloxane polymer intermedia-tes having at least 0.5~ of the silicon atoms chemically combined in accordance with the formula R -Si(~)3 wherein Ra is an aminoalkyl radical, Rx is a radical selected from the group consisting of aminoalkyl sulfona-tes and aminoalkyl carbonates and ~ is a siloxane segmen-t selected from the group consisting of siloxane radicals or a link to the siloxane polymer chain.
Methods for producing these zwitterionic siloxane polymers and aminoalkyl siloxane polymer intermediates are also provided, wherein trifunctional silanes having amino-alkyl radicals r or zwitterions are copolymerized with a hydroxy-terminated siloxane oligomer in -the presence of a catalytic quantity of acid and solvent~
O~JECT OF THE INVENTION
An object of the present invention is to provide aminoalkyl siloxane polymer intermediates and zwitterionic siloxane polymers by utilizing trifllnctional silanes.
Another object of the present invention is to provide a method of incorporating a significant quantity of trifunctional aminoalkyl silane or -trifunctional zwitterionic silane into a siloxane polymer.
Another object of the present invention is to provide zwitterionic siloxane rubbers which obtain their ridigity ~rom both covalent and ionic cross-links.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
-The zwitterionic siloxane polymers and amino-alkyl siloxane polymer intermediates provided by this invention have a siloxane polymer backbone. These siloxane polymers typically have repeating units of a general formula selected from the group consisting of -(R2 SiO)m- and -(R"SiO2)m-- 5 - RD-15,201 wherein R" is a monovalent radical selected from the group consisting of hydrogen, alkyl radicals from 1 to 10 carbon atoms and aryl radicals 1 to 20 carbon atoms, including alkylaryl radicals, and m is an integer from 1 to abou-t 2000. The zwitterions or aminoalkyl radicals replace the monovalent radical R" on the silicone a-toms.
Examples of the siloxane polymer backbones where the zwitterions and aminoalkyl radicals are absent include, polydimethylsiloxane, polydimethyl-co-diphenylsiloxane, poly(methyl phenyl siloxane), etc. At least about 0.5%
of the silicon atoms have the monovalent radical R"
replaced with a zwitterion in the zwitterionic siloxane polymers of this invention. These silicone atoms are chemically combined in accordance with the formula RX-Si(~)3 wherein R is a zwitterion and ~ is either a siloxane radical or a link to the siloxane polymer chain.
~dditional zwitterions may be bound to silicone atoms having a different chemical structure than tha-t of formula I.
In the aminoalkyl siloxane polymer intermediates produced by this invention, at least about 0.5% of the silicon atoms have the monovalent radical R" replaced with an aminoalkyl radica]. These silicon atoms are chemically combined in accordance with the formula R -Si(~)3 II
wherein Ra is an aminoalkyl radical and ~ is as defined above. The ~witterions, RX, that may appear on the silicone atoms of formula I, are aminoalkyl sulfonates and aminoalkyl carbonates. Suitable aminoalkyl sulfonates and aminoalkyl carbonates/ are those of the formulas R'-NH ~~ R SO ~ and -R'-NH2 -R-COO
respectively, wherein R' is a divalent hydrocarbon radical of from 1-20 carbon atoms and R is a divalent hydrocarbon radical of from 2-20 carbon atoms. These divalent - ~ - RD-15,201 hydrocarbon radicals include alkyl radicals, aromatic radicals, alkylaryl radicals, and substituted derivatives thereof. The preferred zwitterions are -the aminoalkyl sulfonate radicals of the formula -(R -TH )n~~ IH2 _ wherein Rl and R2 are selected from a group consisting of diva]ent alkylene radicals of from l-lO carbon atoms and divalent aromatic radicals of from 6-20 carbon atoms, including alkylaryl radicals; R3 is selected from a group consisting of divalent alkylene radicals of from 3 to ~
carbon atoms and divalent aromatic radicals of from 6-20 carbon atoms, including alkylaryl radicals; and n is an integer in the range of 0 to 5.
The preferred aminoalkyl radicals that appear on the aminoalkyl siloxane intermediates are of the formula -(Rl-NH)n-R -NH2 IV
wherein Rl, R2 and n are as previously defined.
The silicon atoms of formulas I and II are of a tertiary structure, i.e., the silicon atom is bonded to three siloxane segments. These siloxane segments, ~, are either siloxane radicals or a link to the siloxane polymer chain. The siloxane radicals are distinguished from the siloxane polymer chain only by their length, the siloxane radi~als being the shortest siloxane segment bonded to the tertiary silicone atom. Where the two shortest segments are of equal length, all of the siloxane segments are considered a part of the siloxane polymer chain.
Both the siloxane radicals and the siloxane polymer chains are of the formu].a - 7 - RD 15,201 ( 2 )m / V
wherein R" is a monovalenk radical select:ed from the group consisting of alkyl radicals of from 1 to 10 carbon atoms and aryl radicals of from 6 to 20 carbon atoms, including alkyl aryl radicals; m is an integer of from 1 to about 2jO00 and R"' is selected from a group consisting of alkyl radicals of from 1 to 10 carbon atoms, the hydroxy radical, tertiary silicon atoms of the formulas RX-Si-O- , and R -si-o-and secondary silicon atoms of the formulas RX-si-o- , and Ra-Si_o_ R" ~' wherein RX, Ra, R" are as defined above and ~' is the hydroxy and alkyl terminated siloxane polymer segments defined by ~.
The preferred zwitterionic siloxane polymers provided by this invention are those wherein the zwitterion, R , is of the ~ormula -CH2-CH2-CH2-NH -CH2-CH2-NH2 ,CH2 C, H2 C,H2 C,H2 C,H2_ C,H2_ and the siloxane radicals and the siloxane polymer chain are of the formula CH3 R"'-(Si-O)m- VI

wherein R"' is limited to the methyl radical and the tertiary silicon atoms of the formula defined above having only the zwitterionic radical, RX, and m is an integer having an avexage value between 30 and 200. The actual values for m may range from about 1 to about 2000 in the preferred zwitterionic siloxane polymers.

_ 8 - RD-15,201 The preferred aminoalkyl siloxane polymer intermediates are those wherein Ra is of the formula and the siloxane radicals and the siloxane polymer chain are of the structure shown in formula VI with R"' heing limited to the methyl radical and the tertary silicon atoms of the formula defined above having only the aminoalkyl radical, Ra, and m is an integer having an average value between 30 and 200.
It is preferable to maintain the number of zwitterions and aminoalkyl radicals bound to the silicon atoms of the siloxane polymer backbones below about 10%.
Where the number exceeds this proportion, the zwitterionic siloxane polymers produced become highly cross-linked and excessively rigid. However, siloxane polymers having more than 10% of their silicon atoms chemically bonded to zwitterions or aminoalkyl radicals are within the scope of this invention, providing the siloxane polymer has at least about 0.5% of the silicon atoms of formula I or II.
The additional zwitterions or aminoalkyl radicals may be bonded eithex to tertiary silicon atoms or secondary silicon atoms of the formulas within the scope of R"' defined above.
The zwitterionic siloxane polymers of this invention typically exhibit a degree of polymerization up to about 2000 with a molecular weight approaching 150/000.
The average degree of polymerization is approximately 1500 with an average molecular weight of about 105,000. The zwitterionic siloxane polymers of this invention may be produced by two different processes. The first process co-polymerizes trifunctional zwit-terionic silanes with hydroxy-endcapped silo~ane oligomers. The second process utilizes the aminoalkyl siloxane polymer intermediates of this invention which are obtained by co-polymerizing a trifunctional aminoalkyl silane with a hydroxy-endcapped ~p - 9 - RD-15,201 siloxane oligomer. The aminoalkyl siloxane polymer intermediate is then treated with an oryanosultone of the formula O

o or an organolactone o the formula o g ¦ VIII

\O
wherein Z is a divalent hydrocarbon species selected from the group consisting of alkalene radicals of from 3 to 4 carbon atoms and aryl radicals of from 6 to 20 carbon atoms, including arylalkyl~radicals. Treatment of the aminoalkyl siloxane precursor wit~ the organosultone or organolactone provides the zwitterionic species.
The same gro~p of hydroxy endcapped siloxane oligomers may be utilized in both syntheses. These hydroxy-endcapped siloxane oligomers are typically of the formula H-(R"2si)m-H Ho-(R''sio2)m-H/H
wherein each R" is as defined above and m is an integer of from 1 to about 2~00. Suitable hydroxy-endcapped siloxane oligomers aIso include branched chained siloxane oligomers that contain tertiary silicon atoms. Other suitable siloxane oligomers are those which already contain ~witterionic or aminoalkyl radicals. These oligomers may be obtained from a process known to the art or by the process provided by this invention. The preferred hydroxy-endcapped siloxane oligomers are the '` :, _10 _ RD-15,201 dimethyl siloxanes having a degree of polymerization of from 3 to about ~00. Other suitable si]oxane oligomers include polydimethyldiphenyl s.iloxanes and poly(me-thyl phenyl) siloxanes.
In the second process, where the zwitterionic siloxane po~ymers are obtained by first producing -the aminoalkyl siloxane polymer intermediates, a trifunctional aminoalkyl silane is copolymerized with the hydroxy terminated siloxane oligomer to obtain the intermediate.
Suitable trifuncti.onal aminoalkyl silanes are those of the formula Ra-Si(ORb)3 hwerein each Rb is independently selected from the group consisting of alkyl radicals of from 1 to 20 carbon atoms and aryl radicals of from 6 to 20 carbon atoms and Ra is as defined above. The preferred trifunctional aminoalkyl silanes are those wherein each Rb is a methyl radical.
The most preferred trifunctional aminoalkyl silanes include N-aminoethyl~ ~-aminopropyl trimethoxysilane and N-aminopropyl trimethoxysilane. Other suitable trifunctional aminoal]syl silanes include N-aminoethyl- ~-aminopropyl triethoxysilane, N-aminoethyl-~ -aminobutyl-trimethoxysilane,

2-aminoethyl-trimethoxysilane, 2-aminoethyl-triethoxysilane,

3-aminopropyl-triethoxysilane, 3-aminopropyl-tributoxysilane, etc.
The trifunctional zwitterionic silanes utilized in the first process for producin~ the z~itterionic siloxane polymers of this in~ention are derived from the trifunctional aminoalkyl silanes described above. These trifunctional zwitterionic silanes can be described by the formula R ~Si(ORb~3 V
wherein Rx and Rb are as defined above. As with the trifunctional aminoalkyl silanes, the preferred trifunc-tional zwitterionic silanes are those wherein _ 11 _ RD-15,201 each Rb is a methyl radical. The most preferred trifunctional zwitterionic silanes include N-(3-propane-sulfonate)- ~-aminopropyl-trimethoxysilane and N-(N-(3-propane sulfonate~aminoethyl) (3-propane-sulfonate)-~ -aminopropyl trimethoxy silane.
It may be desirable to hydrolyze a portion of the alkoxy or aryloxy groups on the silanes prior to copolymerization in accordance with the process described in Canadian Application Serial No. , filed , Florence et al. Hydrolysis of all the functional groups produces a highly relative species which encourages polymerization within itself and may not be desirable. However, hydrolysis of only a portion of the functional groups will not inhibit the copolymerization with the siloxane oligomers completely and permits the pro-duction of zwitterionic siloxane polymers of a high molecular weight.
To produce the zwitterionic siloxane polymers of this invention the ratio of trifunctional silane to siloxane oligomer must be sufficiently large to incorporate zwitterions on at least 0.5 percent of the silicone atoms within the polymers produced. Therefore, the actual ratios are dependent on the size o~ the siloxane oligomer or oligomers that are utilized. The process described herein is also capable of producing zwitterionic siloxane polymers and aminoal~yl siloxane polymer intermediates, having less than .05 percent of the silicone atoms of che formulas I and II, respectively.
The same steps and procedures are utilized when copolymerizing the siloxane oligomers with the trifunctional zwitterionic silanes and the trifunctional aminoalkyl silanes. Copolymeriza~ion is accomplished by reacting a mixture of the starting materials in the presence of an acid catalyst at a temperature within the range oE about 25C to about 100C. It is preferable to let -the reac-tion continue for about 0.5 to 5 hours.

- 12 - RD-15,201 The rate of reaction is dependent on temperature.
The magnitude of the reaction temperature is limited by the degradation of the starting materials. The most preferred reaction -temperature falls in the range of about 40C to abou-t 90C. Copolymerization takes place almost immediately upon addi-ton of the acid catalyst. The reaction approaches completeness within the preferred time range. It may be desirable to place the reaction mixture under a nitrogen a~mosphere to prevent oxidation of the silanes. Alternatively, the reaction can be run under vacuum or another inert atmosphere.
Suitable acid catalysts include the carboxylic acids such as, acetic acid, formic acid, trifloroacetic acid, steric acid, trichloroacetic acid, benzoic acid, phenylacetic acid~ 2-chlorobutanoic acid, 3-chlorobutanoic acid, dichloroacetic acid, 4-chlorobutanoic acid, 5 chlorobutanoic acid, etc. Other acids such as hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen fluoride, perchloric, chloric, chlorous, hypochlorous, p-toluene sulfonic, bromic, carbonic, phosphoric, hypophosphorous, phosphorous, etc. are also suitable.
Quantities of acid sufficient to catalyze the reaction typically fall within the range of about 0.1 to 2 weight percent. However, smaller quantities can be expected to provide catalysis of -this reaction and are deemed to be equivalent to those within the range defined above. Larger ~uantities will also provide catalysts, but do not provide any improvement in results.
Silanes other than trifunctional silanes, such as the difunctional silanes, may be present in the reaction medium. Introducing difunctional zwitterionic or amino-alkyl silanes may be d~sired to increase the number of ionic cross-links without increasing the branched chains of the zwitterionic siloxane polymers produced. Although these difunctional silanes compete for the siloxane oligomers, they do not exclude the trifunctional zwitterionic - 13 - RD-15,201 silanes or aminoalkyl silanes.
Upon copolymerization of the starting materials, a chain stopper may be introduced into the reaction medium to remove the hydroxy-endcaps. Any siloxane oligomer having trialkyl substituted silicone atoms as end groups may be utilized as a chain stopper. Examples of such chain stoppers include~ hexamethyl disiloxane, octamethyl trisiloxane, decamethyl tetrasiloxane, hexamethyl disilizane, etc. The quantity of chain stopper preferably provides a molar ratio of siloxane oligomer to chain stopper of about 1000 to 1. Suitable molar ratiGs provide values for the range of about 100 to 1500. However, -the use of a chain stopper is unnecessary to produce either the aminoalkyl siloxane polymers or the zwitterionic siloxane polymers and may not be desired.
~hen copolymerization provides the aminoalkyl siloxane polymer intermediate to obtain a zwitterionic siloxane polymer, it is necessary to convert -the aminoalkyl radicals to the corresponding zwitterion.
Typically an organic solvent is added to solublize the aminoalkyl siloxane polymers. Suitable solvents include, toluene, benzene, tetrahydrofuran, etc. The reaction mixture is then dried to remove a substantial portion of ~ater along with any alcohol produced by the polymerization reaction and allowed to cool to room temperature. An organo-sultone or organo-lactone is added to the reaction mixture while under a nitrogen atmosphere. Zwi-tterionic species begin to form immediately. After a period of about 10 to 20 hours, substantially all the aminoalkyl radicals are converted to zwitterions. The organic solven-t is then removed from the reaction mixture to allow -the ionic cross-links to form and obtain the zwitterionic siloxane rubber. Suitable organosultones and organo-lactones utilized to produce the zwitterionic species are those o~ formulas VII and VIII. The preferred organosultone is ~-propane sultone and the preEerred - 14 - RD-15~201 is ~ propiolactone. The preferred quantity of the organosultone or organolactone utilized is about 1 molar equivalent to the number of amino groups which appear on the aminoalkylslloxane polymer intermediate.
The following examples are provided to illustrate the process comprising this invention. I~hese examples are not provided with the intent to limit the scope of this invention -to their contents.
Example 1 To a 250 milliliter round bottom flask with mechanical stirrer were added N-(2-aminoethyl)-3-amino-propyl-trimethoxysilane (1.50 grams, 6.76 millimoles) and a hydroxy-terminated polydimethyl siloxane fluid (50 grams;
MW about 15000; DP about 200) under a nitrogen atmosphere.
Acetic acid (10 drops) was added and the conten-ts of the flask were heatecl to 55C with an external oil both.
After 1.5 hours the flask contained a milky white oil of a much higher viscosity than the starting mixture.
Hexamethyldisilizane (1.5 grams) was added and stirring continued at 55C for an additional 0.5 hours. Toluene (450 grams) was added, the flask was equipped with a distillation head and the oil bath temperature was raised to 130C. Approximately 150 grams of distillate was collected, the toluene served to remove any water or methanol produced by the siloxane condensation reactions.
The remaining toluene solution was allowed to cool to 23C
and ~-propane sultone (3.0 grams, 13.5 millimoles) was added in one portion as a solution in 60 grams of dry toluene. The solution was stirred at 23C for 16 hours.
Removal of the toluene by heating in vacuo tllOC, 0-05 millimeters, 1.5 hours) produced a white, translucent, elastomeric, siloxane rubber.
Examp'l'e'2 This example demonstrates a co-polymerization process that is known to the art. To a 250 ml round bottom flask with mecllanical stirrer were added ~-amino-- 15 - ~D-15,201 ethylaminopropyltrimethoxysilane (6 parts), octamethyl-tetrasiloxane (100 parts) and decamethyl-tetrasiloxane (0.84 part). A powdered potassium hydroxide catalyst (0.4 parts) was utilized instead of an acid catalyst as utilized in Example 1. The mixture was stirred and heated to 160 under a nitrogen atmosphere. At about 140C the mixture increased in viscosity and a copious amount of white precipitate was observed. After 18 hours at 160C, the mix-ture was cooled to ambient temperature, diluted with toluene (150 par-ts), stirred for 1 hour, and the solids removed by a vacuum filtration. A yellow oil was obtained by concentrating the solution on a rotary - evaporator and further drying under vacuum (0.1 torr, 75C, 2 hours). Analysis of the oil by infrared spectroscopy indicated a low level of nitrogen incorporation in the polyme~ (N-H stretch at 340 centimeters ).
Infrared analysis of the solid indicated that most of the amine was within the precipitate.
Although the above examples have shown an embodiment of the present invention, further modiEications are possible by those skilled in the art without departing from the scope and spirit of this invention.

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Zwitterionic siloxane polymers having at least 0.5 percent tertiary silicon atoms chemically combined in accordance with the formula Rx-Si-(.theta.)3 wherein Rx is a zwitterion having a chemically combined unit selected from the group of formulas consisting of:
-R'-NH2+-RSO3- and -R'-NH2+-R-COO-wherein R is a divalent hydrocarbon radical of from 2 to 20 carbon atoms, R' is a divalent radical of from 1 to 20 carbon atoms and .theta. are siloxane polymer segments having repeating units of a formula selected from the group consisting of:
-(R2'SiO)m- and -(R''SiO3/2)m-wherein R'' is a monovalent radical selected from the group consisting of hydrogen, alkyl radicals of from 1 to 10 carbon atoms and aryl radicals of from 1 to 20 carbon atoms and m is an integer of from 1 to about 2000.

2. Zwitterionic siloxane polymers of claim 1 wherein the zwitterion, Rx, is an aminoalkyl sulfonate radical of the formula and the siloxane polymer segments, .theta., are of the formula R'' '-(R''2SiO)m-wherein R'' ' is selected from a group consisting of alkyl radicals of from 1 to 10 carbon atoms, a hydroxy radical, a tertiary silicon atom of the formula and a secondary silicon atom of the formula where .theta.' is selected from the group consisting of the hydroxy and alkyl terminated siloxane polymer segments defined by .theta., R1 and R2 are divalent alkylene radicals of from 1 to 10 carbon atoms; R3 is a divalent alkylene radical of from 3 to 4 carbon atoms; R'' is a monovalent radical selected from the group consisting of alkyl radicals of from 1 to 10 carbon atoms and aryl radicals of from 6 to 20 carbon atoms; m is an integer of from 1 to 2000 inclusive and n is an integer of from 0 to 5 inclusive.

3. Zwitterionic siloxanes of claim 1 wherein the zwitterion, Rx, is of the formula and the siloxane polymer segments are selected from the group of formulas consisting of CH2-(R''2Si-O)m- and wherein m is an integer of from 1 to 2000.